The present invention relates generally to body implantable biomedical leads and more particularly to multi-conductor leads.
In the field of implantable electrical leads, a wide variety of configurations have been employed and proposed for providing multi-conductor lead bodies. The two most widely employed approaches are the coaxial design, wherein multiple coiled conductors are mounted around one another, separated by tubular insulative sheaths, as described in U.S. Pat. No. 4,355,646 issued to Kallok and the multi-lumen design, wherein the lead body takes the form of a multi-lumen tube, each lumen carrying a separate conductor, as disclosed in U.S. Pat. No. 5,584,873 issued to Shoberg, et al. Additional alternative approaches have included embedding multiple conductors within the wall of an insulative lead body, as disclosed in U.S. Pat. No. 5,968,087 issued to Hess, et al., U.S. Pat. No. 5,016,646 issued to Gotthardt, et al. and U.S. Pat. No. 5,845,396 issued to Altman et al. An additional alternative approach is disclosed in U.S. Pat. No. 5,935,159 issued to Cross et al, in which individual conductors are separated from one another by means of a central strut having laterally extending projections, serving to space and insulate adjacent conductors from one another, within a tubular outer sheath.
Notwithstanding the variety of lead body designs that have been proposed, there is still a desire to improve the mechanical characteristics and the producability of multiple conductor lead bodies.
The present invention is directed toward providing a multi-conductor lead body having improved mechanical characteristics and improved manufacturability. Lead bodies according to the present invention are manufactured by winding multiple conductors around a generally cylindrical or tubular, insulative core member, and by spacing adjacent ones of the conductors from one another by means of insulative strands or tubes, wound around the core intermediate the conductors. In preferred embodiments of the invention, the conductors may take the form of stranded or cabled conductors, as described in U.S. Pat. No. 5,584,873 issued to Shoberg, et al., cited above and incorporated herein by reference in its entirety. In some embodiments, the core may take the form of an insulative cylindrical or tubular member having a centrally located tensile reinforcement member. In these embodiments, the insulative member may be extruded over the tensile member. In other embodiments, the core may take the form of an insulated coiled conductor, allowing the use of a centrally located stylet to place the lead. In these embodiments, the insulative coating of the coiled conductor may be formed as a separate tubular member or may be extruded in one or two layers, as is desired.
Preferably, the conductors and insulative strands or tubes separating the conductors are sized relative to the core member such that a gap is allowed between the conductors and associated insulative strands or tubes may be physically displaced under loading, improving the crush resistance and durability of the lead bodies. In embodiments employing tubular insulative members separating adjacent conductors, the tubes serve a function similar to that of the compression lumens described in the above-cited Shoberg, et al. patent, further facilitating the ability of the lead to withstand damage due to compression.
According to another aspect of the invention, at least one of the conductors may be electrically and mechanically coupled to an electrode. The electrode may be a defibrillation electrode of the type used in an implantable medical device, and the coupled conductor may be a high-voltage conductor. The electrode may be of an elongated configuration, and positioned along the outer surface of a portion of the conductor. Alternatively, multiple electrodes of this nature may each be positioned along a respective portion of the at least one of the conductors. Openings such as slits fashioned in the jacket of the lead body expose the electrodes so that the outer surface of the electrodes is substantially adjacent to the outer surface of the lead body. This configuration provides a lead of minimal size.